Genes where the sequence of DNA has changed
A change in the arrangement or amount of genetic material in a cell.
Bases, sometimes called nitrogenous bases, are the parts of the DNA molecule that join the two helix strands. They are like rungs on a ladder. There are four bases: adenine (A), thymine (T), guanine (G) and cytosine (C). Each base can only join with one other base; i.e. they join together in pairs: A with T and G with C.
The information in DNA is carried in the sequence of bases. Changes, or mutations, in just one or two bases can scramble the information and mean that the gene does not work properly. If this mutation is in a gene that controls cell division it can trigger the uncontrolled replication of that cell. This faulty gene is copied to all the new cells and so the uncontrolled growth continues. The cells form a tumour.
Only a few bases have to change to cause a mutation in a gene.
To find out more about DNA, genes and mutations click on the links:
Genes and DNA
Researchers are starting to understand the genetic basis of many cancers. This allows improvements in diagnosis, medicines and treatments. It is even becoming possible to see which people may be more likely to develop certain types of cancers.
Cancers linked to known genetic markers
Cancer is quite rare, especially in people under the age of 60. However, some cancers appear to 'run in families'. Researchers have found that certain mutated genes, passed from parents to their children, can dramatically increase the chance of developing a particular cancer. Inheriting the faulty gene does not guarantee that the person will develop cancer but it appears to increase the chance that they will.
Genetic tests can be made to see if a person has inherited a mutated gene that makes them more likely to develop cancer. Some genes, such as P53, are associated with a range of types of cancer, others are specific to just one type.
||Examples of genes associated with specific cancers:
||BRCA2, HPC1, HPC2, HPCX
|Melanoma (skin cancer)
||MSH2, MSH6, MLH1, APC
There are ethical issues around genetic screening. The results can tell a person if they are at a higher than normal risk of developing cancer, but what should be done with this information?
Would you want to know that you were at high risk? What would you do if you did know? How would you react if you were clear of any mutated genes? How should doctors handle this information? Should doctors screen for cancers that cannot be cured?
What decisions would you make? How would you help someone thinking about having a genetic test decide what to do?
For more on the ethical questions relating to inherited disorders, see the Human Genome Project resource.
- Knowing the risk of developing cancer
- Knowing if anything could be passed on to your children
- Being able to make life-decisions knowing the risk of developing cancer
- Being able to monitor for cancer more closely
- May not give a definite answer - only suggest the risk of developing cancer
- Knowing the risks could be stressful and cause other problems
- What happens if there is no cure or treatment for the cancer?
- What do you say to close friends and family?
- How will it influence your life-decisions?